A hemostat is commonly used in surgical procedures to grasp, dissect and clamp tissue. It is typically a simple pliers-like tool that uses mechanical action between its jaws to constrict vessels without cutting them. It is also typical for hemostats to have an interlocking ratchet between the handles so that the device can be clamped and locked in place.
Many hemostats are used in a typical open-surgical procedure. Once vascular tissue has been clamped with a hemostat, it is common for a surgeon to tie a suture around the tissue to close it off permanently prior to removing the hemostat. Several hemostats may be left in the surgical field until the surgeon has the opportunity to tie a suture around each section of clamped tissue.
Small blood vessels have been closed using electrosurgical instruments without the need for sutures. For example, neurosurgeons have used bipolar instruments to coagulate vessels in the brain that are smaller than two millimeters in diameter. These bipolar instruments are typically tweezers-like devices with two arms that can be deflected toward each other to grasp tissue. However, it has been found that these instruments are not capable of sealing blood vessels with diameters larger than about two millimeters. There has been a long-felt need for an easy way to seal larger vessels and vascular tissue bundles without the need for sutures.
It is thought that the process of coagulating small vessels is fundamentally different than vessel sealing. Coagulation is defined as a process of desiccating tissue wherein the tissue cells are ruptured and dried. Vessel sealing is defined as the process of liquefying the collagen in the tissue so that it crosslinks and reforms into a fused mass. Thus, coagulation of small vessels is sufficient to permanently close them. Larger vessels need to be sealed to assure permanent closure.
A number of bipolar electrosurgical forceps and clamps are known in the field. However, these instruments are not designed to apply the correct pressure to a blood vessel to achieve a lasting seal. All of these instrument also suffer from the drawback that they do not combine the simplicity and familiarity of a hemostat with a bipolar electrosurgical circuit.
An example of a bipolar electrosurgical power curve for vessel sealing is disclosed in a U.S. patent application entitled, “Energy Delivery System for Vessel Sealing,” Ser. No. 08/530,495, filed Sep. 19, 1995, and is hereby incorporated by reference and made a part of this disclosure.
A U.S. patent application entitled, “Vascular Tissue Sealing Pressure Control and Method,” Ser. No. 08/530,450, filed on Sep. 19, 1995, discloses another surgical tool for sealing vessels, and is hereby incorporated by reference and made a part of this disclosure.
One of the important advances of the present system is that it can effectively seal larger vessels of a patient without leaving any foreign material in the body of the patient. The present system is capable of sealing vessels as large as ten millimeters in diameter. Another advantage of the present system is that the surgeon can visually inspect the integrity of the seal.
This invention works with a combination of pressure and controlled application of electrosurgical energy to achieve the desired result. Therefore, the system requires a tool to grasp and apply an appropriate amount of pressure to the tissue of the patient. The term “pressure” refers to the closure force on the vessels or other tissue that is applied by the end effectors of the tool. The tool must also be capable of conducting electrosurgical energy to the tissue concurrently with the application of pressure.
An electrosurgical generator is used to generate the electrosurgical energy. The electrosurgical energy is preferably applied in a specified manner by using an automatic control system. The control system regulates the output current and the output voltage of the electrosurgical generator in a manner that provides optimal vessel sealing.
One of the advances of the present invention is that a high current is applied to the tissue in order to melt the proteins. The high current is important for its effect on the tissue. Similarly, the output voltage is regulated to reduce sparking and localized tissue heating. The voltage is preferably kept below one hundred sixty volts RMS, and in the preferred embodiment is kept below one hundred twenty volts RMS.
Earlier attempts to seal vessels with electrosurgery were unsuccessful in part because a relatively low current was applied. The present invention may draw a maximum current in excess of two amperes RMS through the tissue. This level of output current is higher than the design capabilities of many presently available electrosurgical generators.
Charring of the tissue can be avoided by terminating the flow of electrosurgical energy to the tissue at an appropriate time. There are several techniques for determining when to terminate the electrosurgical energy. One technique is to monitor the impedance of the output load on the electrosurgical generator. When the impedance reaches a certain level, preferably above one thousand ohms, the electrosurgical energy should be terminated.
Another technique is to monitor the phase angle between the output voltage and the output current. Energy delivery to the surgical tool should be terminated preferably when the output current leads the output voltage by an angle greater than approximately fifty degrees.
A third technique for determining when to terminate the electrosurgical energy is to monitor the output current. As the tissue desiccates, the amount of electrical current flowing through the tissue decreases. The generator may terminate the energy delivery to the surgical tool when the output current drops below approximately 200 milliamperes RMS.
It is preferable to maintain pressure on the vessels or tissue of the patient for a short time after the electrosurgical energy has been substantially terminated. This allows the tissue to cool in its newly sealed state. An audible tone indicator in the generator is preferably available to indicate to the surgeon when it is appropriate to release the pressure on the tissue. The time delay may be up to five seconds after terminating the energy delivery to the surgical tool.
In the preferred embodiment there are four main steps for using the tissue sealing system. The first step may include applying and maintaining pressure on the tissue. The second step may include rapidly heating the tissue with electrosurgical energy. The third step may include lowering the energy which is delivered to the tissue so that the tissue will desiccate without charring. The final step may include terminating the electrosurgical energy delivery to the tissue so that the tissue is allowed to cool while still under pressure.
An automatic control system is preferably located within the electrosurgical generator and has, as one of its functions, the ability to automatically transition through the different levels of electrosurgical energy delivery. In an alternative embodiment, the power delivery to the surgical tool may not have discrete, step-wise levels. Instead, the power delivery may be a smooth function which initially delivers a high current, and then transitions to a lower power lever to desiccate the tissue, followed by termination of the power delivery when the impedance of the tissue rises above approximately one thousand ohms.
What follows is a summary of the various embodiments of the invention. The preferred embodiment of the electrosurgical energy delivery system is used for sealing vessels and other tissues of a patient. The system comprises a generator, a surgical tool, and means for controlling the level of electrosurgical energy which is delivered to the tissue.
The generator is preferably capable of delivering a controlled level of high frequency electrosurgical energy. The output of the generator may be characterized as having an output voltage and an output current which are each regulated in the preferred embodiment. The generator in the present system could limit the output voltage to a value below one hundred sixty volts RMS, and most preferably would be limited below one hundred twenty volts RMS. One of the reasons for limiting the output voltage is to avoid sparks and arcing which cause local high temperature zones in the tissue, and can also result in the tissue sticking to the electrodes. Another disadvantage of arcing is that it may result in transection of the vessel.
The surgical tool is most preferably connected to the generator output for receiving the electrosurgical energy. The surgical tool may take the form of forceps, clamps, or any instrument with articulating members for grasping tissue.
In a bipolar configuration, one member of the surgical tool will be electrically connected to be an active electrode, and another member of the surgical tool will be electrically connected to be a return electrode. Alternatively, in a monopolar arrangement, the surgical tool may be electrically connected to only one electrical pole of the generator, while the patient is electrically connected to the other electrical pole. While the members are grasping tissue, electrosurgical energy from the generator will flow in circuit through the tissue.
In the preferred embodiment, there are means for controlling the level of electrosurgical energy delivered to the surgical tool. The level of electrosurgical energy is controlled such that the vessels and other tissues are sealed as they are grasped by the members of the surgical tool. The level of electrosurgical power may refer to the RMS power output of the generator, which may be a function of output voltage, output current, frequency, and duty cycle.
The surgical tool may also have means for applying pressure to the vessels and other tissues between the members concurrently with the application of the electrosurgical energy. The pressure application means can take of the form of a latch or indent which holds a known spring force against the members of the tool. There may be several selectable levels of pressure available from the surgical tool. For example, it may be desirable to apply a high level of pressure to arteries and vascular tissue, and a lower level of pressure to veins.
During an operation, the surgeon may grasp a vessel with the surgical tool and operate the mechanisms on the tool to apply the desired level of pressure to the vessel. Once the pressure has been applied to the vessel, the surgeon may activate the electrosurgical energy. The generator applies the appropriate amount of electrosurgical energy according to a specified power curve.
There are several methods for feedback control to the generator. Feedback control is important because the transition points in the power curve are scheduled to occur according to the state of the tissue. In addition, it would be undesirable to apply too much energy to the tissue and thus cause charring and sticking. Several parameters may be monitored for purposes of feedback control. These parameters include the impedance of the tissue, the phase angle between the output voltage and output current, the level of output current flowing through the tissue, and the temperature of the tissue.
It is preferable for the generator to have means for at least approximating impedance of the vessels and other tissues of the patient as they are grasped by the members of the surgical tool. For example, one way to approximate the impedance of the tissue is to assume that the impedance is mostly resistive, and thus make the approximation by dividing the output voltage by the output current. Other numerical techniques for approximating impedance are available so that a long division need not be performed. One such approximation technique is to scale the output voltage and output current appropriately so that a range of impedance may be estimated by mere comparison and bit shifting in a digital circuit.
Impedance of the tissue is a good indicator of the state of desiccation of the tissue. One reason for having an estimate of the impedance is to control the level of electrosurgical energy so that it is substantially terminated when the impedance of the vessels and other tissues rises above approximately one thousand ohms. In certain embodiments of the invention, it may be convenient to terminate the energy delivery to the surgical tool when the estimate of impedance rises above 2048 ohms.
The preferred means for controlling the level of electrosurgical energy comprises several stages. The first stage is a rapid power delivery function for rapidly increasing the power delivery to the vessels and other tissues until a first impedance breakpoint is reached. The second stage is a constant power delivery function for maintaining a constant power delivery to the vessels and other tissues until proteins in the vessels and other tissues have melted. The third stage is a low power delivery function for maintaining a low power delivery to the vessels and other tissues until a second impedance breakpoint is reached. In the preferred embodiment, the transitions between the stages are executed automatically in the generator without further input from the surgeon. The impedance breakpoints are preferably 16 ohms for the first breakpoint, and 2048 ohms for the second breakpoint.
A method for sealing vessels and other tissues of a patient is also claimed. The method comprises the steps of: applying pressure to the vessels and other tissues of the patient; applying a first level of electrosurgical energy to the vessels and other tissue sufficient to melt proteins in the tissue; applying a second level of electrosurgical energy to the vessels and other tissue sufficient to cause desiccation without charring; reducing the electrosurgical energy substantially for a length of time sufficient to allow the vessels and other tissues to cool into a new compressed form; and relieving the pressure on the tissue. The step of relieving the pressure on the tissue may occur after a delay of less than five seconds. Additionally, there may be a step of creating an audible indication after the delay is over.
An additional step in the method may be approximating impedance of the vessels and other tissues. If this step is carried out, there may be another step of terminating the second level of electrosurgical energy after the impedance of the vessels and other tissues rises above approximately one thousand ohms.
FIG. 1′ is a schematic diagram of an electrosurgical vessel sealing system.
FIG. 2′ is a set of power curves which represent the electrosurgical power delivered to the tissue as a function of the tissue impedance.
An electrosurgical energy delivery system 10′ is shown in FIG. 1′. The system 10′ is used for sealing vessels and other tissues of a patient 13′, including ducts, veins, arteries, and vascular tissue. The system 10′ comprises an electrosurgical generator 11′, a surgical tool 12′, and means to control the output of the electrosurgical generator 11′ such that it works cooperatively with the surgical tool 12′ to effectively seal vessels and other tissues of a patient 13′.
The electrosurgical generator 11′ must be capable of delivering a controlled level of electrosurgical output power. The output power may be controlled by adjusting the output current and the output voltage. The surgical tool 12′ is electrically connected to the generator 11′ for receiving the electrosurgical power. The surgical tool 12′ has members 14′, or end effectors, capable of grasping the vessels and other tissues of the patient 13′. The members 14′ are also capable of applying and maintaining a relatively constant level of pressure to the vessel.
The electrosurgical generator 11′ must have means for automatically controlling the level of electrosurgical power delivered to the surgical tool 12′. This can be in the form of a feedback control system. In the preferred embodiment, there are also circuits for limiting the output current and the output voltage. In one embodiment, an adjustable high voltage power supply is used to adjust an RF output stage for controlling the electrosurgical output.
The power output of the generator 11′ is described in terms of a power curve, and a preferred embodiment is shown in FIG. 2′. The power curve may be described in terms of several stages. The stages may be discrete, or may be approximated by a smooth continuous function. In the first stage of the power curve, the electrosurgical generator 11′ delivers output power even at impedances below approximately sixteen ohms, and holds a high power lever until the proteins in the tissue have sufficiently melted. During this first stage, the output current is allowed to increase to a maximum amplitude which is typically greater than two amperes RMS. It has been found that a high current is important for effective vessel sealing.
After the first stage, the electrosurgical power is lowered to a level sufficient to desiccate the vessels and other tissues. The lower power enables the desiccation to occur without charring the tissue.
A final stage involves allowing the tissue to cool into its new sealed form. During this final stage, the application of electrosurgical power to the tissue is substantially terminated. After the tissue has cooled, the closure force is released. The length of time for cooling is typically less than five seconds. In the preferred embodiment, a audible tone would indicate to the surgeon that the sealing process was complete. The surgeon would thereafter release the vessel from the surgical tool 12′.
It is thought that the initial high current causes proteins in the tissue to melt. The subsequent lower power delivery to the tissue allows the proteins to cross link. As the tissue cools, the new cross linked tissue will form a permanent seal of the vessel.
The surgical tool 12′ may further comprise an index for selectively applying multiple levels of closure force between the members 14′. For example, arteries will require a greater closure force than veins. It has been found that a closure force of greater than 1500 grams is effective for sealing arteries. A closure force of less than 500 grams is effective for sealing veins.
In the preferred embodiment, the surgical tool 12′ will have a spring that compresses to hold a closure force on the members 14′. The index is mechanically linked to the spring such that each successive stop on the index holds a higher compression on the spring. The spring will not begin to compress until the members 14′ encounter resistance to closure.
In the preferred embodiment, the generator 11′ further comprises means for approximating impedance of the vessels and other tissues of the patient 13′ as they are grasped by the members 14′ of the surgical tool 12′. The calculation of impedance can require long division and other lengthy mathematical manipulations. There are a variety of techniques for making a quick approximation of impedance which would be sufficient for purposes of controlling the power output of the electrosurgical generator 11′. For example, comparison of the output voltage with the output current can yield an estimate of the impedance without resorting to long division.
The impedance of the tissue gives an indication of the state of desiccation of the tissue. By monitoring impedance, the generator 11′ can provide the appropriate amount of electrosurgical energy without charring the tissue. For example, the power control circuit includes a power cutoff function for substantially terminating the power delivery to the surgical tool 12′ when the impedance of the vessels and other tissues rises above approximately one thousand ohms.
The power control curves shown in FIG. 2′ represent the electrosurgical output of the generator 11′ as a function of tissue impedance. At low impedances, the electrosurgical power is increased by rapidly increasing the output current, as shown by the segment labeled A. The increase in electrosurgical power is terminated after a first impedance breakpoint is reached. The first impedance breakpoint is shown as Point 1 in FIG. 2′. In the preferred embodiment, this point is typically below 20 ohms.
Next, the electrosurgical power is held approximately constant until proteins in the vessels and other tissues have melted. The impedance at which this segment ends will vary in accordance with the magnitude of the RMS power. Thus, where the maximum RMS power is approximately 125 Watts, this segment will end at approximately 128 ohms. This is shown as the segment labeled B in FIG. 2′. Where a lower power is used, such as 75 Watts, the segment may end at 256 ohms. This is shown as the segment labeled C in FIG. 2′.
Next, the output power is lowered to less than half of its maximum value. The low power delivery is terminated when a second impedance breakpoint is reached. In the preferred embodiment, the second breakpoint is approximately at 2048 ohms.
As an alternative to using impedance to determine the second breakpoint, the phase angle between current and voltage may be used. In this alternative embodiment, the generator 11′ includes means for substantially terminating the power delivery to the surgical tool 12′ when the output current leads the output voltage by an angle greater than approximately fifty degrees.
In yet another alternative embodiment, the generator 11′ will terminate the power delivery to the surgical tool 12′ when the output current drops below approximately 200 milliamperes RMS.
It is desirable to have the generator 11′ limit its output voltage at all times to less than one hundred sixty volts RMS. The reason for keeping the output voltage low is to prevent arcing and the resulting localized tissue burn spots which might cause the tissue seal to fail.
A method for sealing vessels and other tissues of a patient 13′ comprises the following steps. First, apply a closure force to the vessels and other tissues of the patient 13′ sufficient to substantially close off the interior passages of the vessels or tissue. Second, apply a first level of electrosurgical power to the vessels and other tissues, wherein the peak output current is greater than two amperes and the peak output voltage is less than one hundred sixty volts RMS. Third, reduce the electrosurgical power to a second level which is less than half of the first level. Fourth, apply the second level of electrosurgical power to the vessels and other tissue of the patient 13′ for a length of time sufficient to cause desiccation without charring. Fifth, reduce the electrosurgical power substantially for a length of time sufficient to allow the vessels and other tissues to cool into a new compressed form. Sixth, relieve the closure force on the tissue.
The fifth step of reducing the electrosurgical power can be accomplished either by terminating the power to the surgical tool 12′, or by reducing the power to the surgical tool 12′ to a very low level. In one embodiment, the electrosurgical energy would be terminated completely so that the tissue 13′ would cool in the fastest time possible. In an alternative embodiment, the generator 11′ would continue to output approximately one watt of power for the purpose of maintaining a closed circuit with the tissue 13′ until the tissue has cooled into its compressed form.
In the preferred embodiment, the method for sealing vessels and other tissues will have the additional step of periodically approximating the impedance of the vessels and other tissues. This step will enable a control system in the generator 11′ to adjust the output power in accordance with the impedance of the tissue. For example, the step of applying a second level of electrosurgical power would be terminated after the impedance of the vessels and other tissues rises above approximately one thousand ohms.
Alternatively, the step of substantially terminating the power delivery to the surgical tool 12′ can occur when the output current leads the output voltage by an angle greater than approximately fifty degrees. An additional alternative is to terminate the power delivery to the surgical tool 12′ when the output current drops below approximately 200 milliamperes RMS.
In the preferred embodiment, there are additional steps of limiting the output voltage to a value below approximately one hundred sixty volts RMS, and audibly indicating when the closure force on the vessels and other tissues should be removed. The audible indication occurs after substantially reducing the level of electrosurgical power, and after a further delay of less than five seconds.
U.S. Pat. No. 371,664 discloses a pair of electric forceps with positive and negative electric poles located on the jaws.
U.S. Pat. No. 728,883 discloses an electrothermic instrument in which electricity is used to heat one of the jaws of the instrument.
U.S. Pat. No. 1,586,645 discloses a bipolar instrument for coagulating tissue.
U.S. Pat. No. 2,002,594 discloses a bipolar laparoscopic instrument for treating tissue, whereby coagulation and cutting of tissue can be performed with the same instrument.
U.S. Pat. No. 2,176,479 discloses an instrument for finding and removing metal particles. The jaws of the instrument are designed to complete an electrical circuit when conductive material is placed therebetween. An insulated pivot and an insulated ratchet are used to prevent a short circuit.
U.S. Pat. No. 3,651,811 discloses a bipolar electrosurgical instrument for cutting and coagulating tissue.
U.S. Pat. No. 4,005,714 discloses bipolar coagulation forceps with jaws that open and close by way of an actuating sleeve.
U.S. Pat. Nos. 4,370,980 and 5,116,332 disclose an electrocautery hemostats wherein the hemostatic clamping function and the electrocautery function may be accomplished with a single instrument. Monopolar electrosurgical designs are shown and described.
U.S. Pat. No. 4,552,143 discloses a family of removable switch electrocautery instruments, including an electrocautery hemostat. Monopolar electrosurgical designs are shown and described.
U.S. Pat. No. 5,026,370 discloses an electrocautery forceps instrument having an enclosed electrical switching mechanism. Monopolar electrosurgical designs are shown and described.
U.S. Pat. No. 5,443,463 discloses coagulating forceps having a plurality of electrodes.
U.S. Pat. No. 5,484,436 discloses bipolar electrosurgical instruments for simultaneously cutting and coagulating tissue.
The article, “The Mechanism of Blood Vessel Closure by High Frequency Electrocoagulation” discloses experiments upon the blood vessels of dogs. The sentence starting on the last line of page 823 describes “an electrode forceps, each of the blades being insulated form the other and each connected to a terminal of the high frequency generator.”
The article, “Studies on coagulation and development of an automatic computerized bipolar coagulator” discloses on page 150 that, “It was not possible to coagulate safely arteries with a diameter larger than 2 to 2.5 mm.” On page 151, line 5, it is noted that “Veins can be coagulated safely up to a diameter of 3 to 4 mm.”
Russian Patent 401,367 discloses a bipolar instrument with a linkage that brings the working jaws together in a parallel manner.
Prior disclosures have not provided a design for a bipolar electrosurgical instrument capable of conveniently applying a constant pressure, from a calibrated spring-loaded source held by a ratchet, that is sufficient to seal vessels and vascular tissue.